In applying a light source to a light emitting device, various attempts have been made to collect or diffuse light emitted from a light source to a spot according to applications of the light emitting device. For example, in case of a backlight unit used in displays such as notebook computers, monitors, mobile phones, TVs, an optical member that diffuses light emitted from a light source is used in order to secure uniform light emissions, while reducing an amount of light sources mounted thereon. In applying an optical member to change light distribution characteristics or an angle of beam spread, matching positions of a light source and an optical member may affect light characteristics. Thus, in the art, various attempts have been made to increase precision in matching positions of a light source and an optical member.